The NICHD is planning to support a case-control study of the Sudden Infant Death Syndrome (SIDS) among families served by the Kaiser Permanente Medical Care Programs of Northern (KPNC) and Southern California (KPSC). It is anticipated that 250 SIDS cases and 500 living control infants will be enrolled within the study period. The objectives of the study are (1) to determine the risks of SIDS associated with sleeping in prone, side or back sleeping positions, (2) to identify risk factors that modify the association of sleeping-position with SIDS risk, and (3) to determine changes in sleeping position and SIDS rates among the population of KPNC and KPSC.